Different types of MEMS electrostatic micro-actuators have been used to achieve Autofocus (AF) and Optical Image Stabilization (OIS) in miniature cameras. U.S. Pat. No. 9,264,591B2 discloses a MEMS electrostatic actuator to achieve OIS and AF by providing a multiple of degrees of freedom (DOF) motion to move the image sensor. The actuator also utilizes mechanical flexures/springs between the driving comb electrodes and the load stage for the purpose of amplifying the rotational strokes and to reduce the coupling effect between motion along different axes. Such structure, elastic flexures between the load and driving electrodes, significantly reduces the electrostatic forces acting on the load. It also introduces mechanical coupling between different motions as one set of springs (i.e. four mechanical springs) are connected to a single load stage and are responsible to move the load stage along multiple axes. When the driving electrodes move the load along one axis of motion by exerting a force transmitted to the load through two springs, the other two springs connected to the load transmit the motion to other not-moving electrodes and vice versa. Such mechanical coupling is undesired in MEMS actuation.
Another MEMS electrostatic actuator is used to achieve OIS in miniature cameras and presented in U.S. Pat. No. 9,578,217B2. The actuator is able to move the image sensor along 3-DOF in-plane motion, i.e., translation along the x and y axes and rotation about the z-axis to achieve OIS. This actuator is unable to provide translational motion along the optical axis z to achieve autofocus, which makes its use in compact cameras. Therefore, it has limited benefits as it provides only a partial functionality for a camera (achieves OIS only and not AF).
There is an increasing need for a single actuator that is able to provide large force and totally decoupled motion along the 3 axes (x, y, and z) such that autofocus, optical image stabilization and super resolution imaging are all enabled using the single MEMS actuator.